Grinding machine

ABSTRACT

A grinding machine wherein sparkout grinding is carried out with small increments of cross-feed introduced every time the load drops to a predetermined value.

United States Patent Uhtenwoldt 1 GRINDING MACHINE [72] Inventor:Herbert R. Uhtenwoldtfworcester,

Mass.

[73] Assignee: Cincinnati Milacron-Heald Corp.,

Worcester, Mass.

221 Filed: May 17,1971 21 ApplQNo; 143,926

[.56] References Cited UNITED STATES PATENTS Kumholm ..51/l65.93

[451 Nov. 21, 1972 3,403,480 10/1968 Robillard' ..5l/l65.87 3,534,50910/1970 Hatstat ..5l/l65.9l

Primary Examiner-Harold D. Whitehead Attorney-Norman S. Blodg ett [57]ABSTRACT A grinding machine wherein sparkout grinding is car- .ried outwith small increments of cross-feed introduced every time the load dropsto a predetermined value.

5 Claims, 4 Drawing Figures ,-58 STEPP/NG 1 00 lilll'i'i'iliiii. 59*EPATENTED NOV 2 1 I872 SHEET 1 0F 3 58 STEPP/NG MOTOR "I *iiii FIG. I

HERBERT R. UH TENWOLDT IN VE N TOR.

BACKGROUND OF THE INVENTION It is the usual practice in grinding toprovide a sparkout period at the end of a grinding cycle. This is ac-'complished by terminating cross-feed and allowing grinding to take placeunder the impetus of the deflection of the spindle, which deflection canbe appreciable, particularly in an internal grinding machine. Such asparkout period relieves the workpiece surface of any taper that may bepresent due to spindle bending or deflection and also provides for abetter surface finish because of the light pressure between the wheeland the workpiece. It also allows the final size of the workpiece to beapproached gradually, so that more accurate gaging can take place.

Asthe demands on grinding machines increase for smaller tolerance ontaper, size, and finish, the conventional sparkout leaves something tobe desired. First of all, final gage size terminates the sparkout. Theamount of taper in the workpiece bore (for internal grinding) depends onthe amount of deflection left in the spindle at the final size point,and this depends, in turn, on the amount of deflection at the beginningof sparkout. This starting deflection varies from workpiece toworkpiece, so that the final taper varies also. If one attempts toovercome this deficiency by allowing the wheel to grind until deflectionis entirely removed from the spindle, the grinding cycle becomes verylong, and this is unacceptable in the case of an expensive automaticgrinding machine, because it increases the amount of labor cost,overhead, and capitalization applicable to each workpiece.

It has been found, furthermore, that the best surface finish is obtainedwhen the finish grinding takes place with an appreciable force betweenthe wheel and workpiece, rather than allowing the force to fall off to avery small value, as is true in the conventional sparkout. Such anappreciable force is, however, substantially less than the amount usedin controlled force grinding where the force used is as high as isfeasible without destruction of the wheel. Nevertheless, many attemptshave been made in the past to provide a relatively low, but,nevertheless, appreciable value of force during the finish period of thegrinding cycle. Since the controlled force used in the roughing portionsof the cycle are produced by using a hydraulic cylinder and controllingthe oil pressure and drain restriction for the cylinder, it was naturalto try to maintain this low-value force by this means. However, itproved to be unfeasible to hold the forces constant within the requiredlimits, because of the conduits, grinding swarf, guards, etc. It wasalso suggested that the low-value force could be obtained by swivellingthe wheelhead, but experiment proved that the amount of swivel necessaryto take care of the deflection difference between finishing with a largewheel and finishing with a small wheel is infinitesimally small, i.e.,in the order of magnitude of the deflection resulting from a forcechange of one pound. Maintaining forces within a S-pound value hasproved to be impossible, especially under shop conditions. These andother difficulties experienced with the prior art devices have beenobviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide agrinding machine in which sparkout is feasible even under closetolerances of size, taper, and surface finish.

Another object of this invention is the provision of a grinding machinein substantially constant force is obtainable during finish grinding.

A further object of the present invention is the provisionofa grindingmachine in which the taper in successive workpieces is maintained at apreselected value.

It is another object of the instant invention to provide a grindingmachine in which good repeatability of taper and surface finish isobtainable.

Astill further object of the invention is the provision of a grindingmachine having means for maintaining low values of controlled forcebetween the abrasive wheel and the workpiece.

It is a further objectof the invention to provide a grinding machinewherein short grinding cycles are possible without exceeding selectedtolerances on taper and finish.

It is a stillfurther object of the present invention to provide agrinding machine in which surface finish does not change due to thereduction in diameter of the abrasive wheel as it wears and is dressedfrom the large new wheel to the small worn wheel.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification .and covered by the claims appendedhereto.

SUMMARY OF THE INVENTION A In general, the invention has to do with agrinding machine having a feed mechanism for bringing about relativemovement between the wheelhead table and the workhead table to causeengagement of the abrasive wheel with the workpiece with controlledforce during most of the grinding cycle and to shift to sparkoutgrinding for the remainder of the cycle. The feed mechanism includes anactuator capable of bringing about the relative movement in anincremental manner during the sparkout grinding. A control is provided,including a device for measuring the load on the wheelhead motor,connected to the actuator to advance the wheel toward the workpiece eachtime the load drops to a predetermined value.

More specifically, a gage is used to terminate the grinding cycle when apredetermined workpiece size has been reached. The actuator is astepping motor operative to produce incremental motion in response tothe receipt of electrical pulses, and the said device operates a gate atthe predetermined load to introduce a preselected number of pulses tothe actuator.

DESCRIPTION OF THE DRAWINGS The character of the invention, however, maybe best understood by reference to one of its structural forms,

1 as illustrated by the accompanying drawings, in which:

FIG. 4 is a chart showing the relationship of grinding force, wheelheadtable position, and workpiece size during a grinding cycle.

DESCRIPTION OF THE PREFERRED EMBODIMENT I Referring first to FIG. 1,wherein are best shown the general features of the invention, thegrinding machine, indicated generally by the reference numeral 10, isshown as consisting of a base 1 1 on which is mounted a workhead table12 and a wheelhead table 13. Also mounted on the base 11 is a controlcabinet 14.-

Mounted on the table 12 is a workhead 15 carrying a workpiece 16 which,for the purpose of illustration, is shown as the outer race of a rollerbearing whose bore is to be finished. Mounted on the table 13 is awheelhead 17 driven by an integral motor and carrying a rotatablespindle 19, the outer end of which carries an abrasive wheel 21. At thefront of the table 13 is mounted a feed box 22, while mounted on theworkhead table 12 is a diamond dressing unit 23 as well as loadingmechanism (not shown).

The grinding machine 10 is similar to that shown in the copending patentapplication of Robillard, Ser. No. 879,785, filed on Nov. 25, 1969. Themachine is provided with a cross-feed hydraulic cylinder 26, the frontof a retractable stop mechanism 27 operated by a stepping motor 28, andvarious other controls associated with the machine. The workhead 15 hassupport shoes (not shown) which engage and support the outer surface ofthe workpiece 16. One end of the workpiece is engaged and driven by atubular drive platen 31 which is suitable rotated by a motor 32. Locatedinternally of the workpiece bore is a gage 33 which takes a continuousreading (during certain portions of the grinding cycle) of the size ofthe bore in the workpiece that is being ground. The other end of theworkpiece is engaged by clamping rollers (not shown), in the usual way.

It can be seen that a compensation slide 43 is engaged at the rear by aball screw 57 operated by a stepping motor 58. In the description thatfollows, the stepping motor 58 will be spoken of as stepping motor No.1, while the stepping motor 28 will be considered as stepping motor No.2. The workhead table 12 is mounted on ways 59 for movementlongitudinally of the axis of the workpiece, and this motion is broughtabout by the operation of a hydraulic cylinder 61. By means of the usualcontrols, the table can be reciprocated during grinding in the usualway. The wheelhead table 13 is mounted on ways 62 for transverse motion.The gage 33 is shown as being of the pneumatic type having a leadextending outwardly to the control cabinet 14. The motor in thewheelhead 17 is provided with a contact-type load meter 110 having acontact hand 11 1 and an adjustable contact 112.

FIG. 2 shows the interior of the retractable stop mechanism 27, and italso shows the manner in which the feed box 22 is provided with anobservation window 36. The stop mechanism 27 is bolted to the front ofthe wheelhead table 13 which, in turn, is mounted for transverse slidingmotion over the base 11. A contact element 37 is slidably mounted in thehousing of the stop and is propelled transversely by rotation of a ballscrew 38. The ball screw is, in turn, mounted in bearings 39 and isdriven by a worm gear 41.

The contact element is positioned to engage, on occasion, with ahardened element 42 mounted on a forwardlyfacing surface of a secondaryor compensating slide 43. A horn 44 extends downwardly from thewheelhead table 13 and is provided with a contact ele ment 45 adapted onoccasion to engage a hardened metal element 46 mounted on a rearwardlydirected surface of the compensating slide 43. The worm gear- 41 and,therefore, the ball screw 38, is driven by the stepping motor 28 and ismanually adjustable by means of a knob 47. A manual compensating knob 48extends from the front of the machine.

FIG. 3 is helpful in understanding the operation of the invention.Hydraulic pressure originating in a source 64 is passed on to the feedcylinder 26 which operates through a mixer 65 to produce the controlledforce grinding process 66. These forces make themselves felt at a mixer67 which operates through the spring constant, K, of the system(indicated by the box 68) which, in turn, feeds a force signal into themixer 65. The grinding process also is affected by a crossslide damper69 receiving force in the grinding process 66 and entering into themixer 65. At the same time, a pulse generator 71 operates the steppingmotor No. 2, and this is effective through the gear train and ball screw38 to operate through the mixer 67 on the system spring constant box 68.Retraction and reset control 72 controls the flow of pulses from thepulse generator 71 to the stepping motor No. 2. Similarly, a pick orrate mode selection 73 operates through a feed-rate control 74'to alsoregulate the flow of pulses from the generator 71 to the stepping motorNo. 2. The grinding process 66 is effected by the compensation slide 43which, in turn, is regulated by the stepping motor No. 1

operating through a gear train and ball screw. A pulse generator 75 iscontrolled by a logic circuit 76 which, in turn, operates through apulse-to-step converter 77 in the stepping motor control, a variation inoperation being possible by means of the new wheel reset control 78.Feedback takes place between the output of the pulse generator 75 andthe inputof the logic circuit 76 through a binary code decimal counter79 (BCD counter). The contact hand 111 of the load meter is connectedthrough an electrical source 113 to ground; the contact 112 is connectedto a timer 114 having an output relay 115 whose contact 116 is normallyopen and connected between the feed rate control 74 and the logiccircuit. The timer closes the contacts 116 when the hand 111 engages thecontact 112 as the load drops. It maintains the contacts closed for apreset interval of time and allows pulses to pass to motor 2 during thatinterval. It, therefore, acts as a gate for stepping motor pulses.

The general operation of the machine can be best understood by examiningFIG. 4. The cycle shown and described is one which might be used togrind a bore in a particularly difficult workpiece having a very hardsurface to be ground. Referring first to the WHEEL- HEAD TABLE POSITIONgraph in the center, it can be seen' that the workhead table 12 movesinwardly on rapid traverse to the point A, so that the abrasive wheel 21lies within the workpiece 16. The hydraulic crossfeed cylinder 26 isenergized to cause the wheelhead table 13 to move transversely and tobring the wheel into engagement with the surface to be finished.Engagement of the abrasive wheel 21 with the surface of the workpiece 16takes place at the point B, .and the workhead table beginsreciprocation, while the wheel is advanced laterally into the workpieceunder the hydraulic pressure in the cylinder 26 on a controlled forcegrinding operation. This operation is a rough grind that consists inrounding up the bore in the workpiece and removing substantial amountsof material from the surface. Eventually, a point C is reached, asdetermined by a dress timer which had started at the point A. Aretraction of the wheelhead table rear- 7 wardly to the point D takesplace to relieve the deflection in the spindle l9 and a further actionby means of the cylinder 26 carries the wheelhead forwardly to the pointE where the horn 44 engages the rearwardly facing surface of thecompensation slide 43. The compensation slide is then moved rearwardlyby introducing a suitable number of pulses into the stepping motor No.I; this also has the effect of carrying the wheelhead table 13rearwardly a short compensating distance. The workhead table 12 is thenoperated by the cylinder 61 to cause the diamond dressing unit 23 tomove past the wheel 21 to dress the wheel, at which time the point G isreached. The wheelhead 13 is then moved inwardly by the cylinder 26, sothat the wheel engages the workpiece at the point H which, because ofthe retraction from point C to point D that previously took place, meansthat the wheel begins grinding without cutting air. Another rough grindtakes place to the point I where a second dress timer times out andcalls for another dress. Retraction takes place to the point J, whichretraction is the same as from the point C to the point D. Then, thewheelhead table 13 is moved back to the point K, compensation takesplace to the point L, and a traversing of the workhead table 12 causes adress to take place to the point M. The wheelhead table moves inwardlyagain, engaging the workpiece at the point N, and a grind takes place ata low force controlled force process to the point 0. The point 0 isindicated by the gage 33 as having arrived, and a signal takes place,stopping the grinding operation and introducing a retraction movement tothe point P. This retraction is considerably less than the retractionfrom the point C to the point D, or from the point I to the point Jbecause the low force cutting during this finish portion of the cyclehas caused a smaller deflection of the spindle 19. After the retractiontakes place, the wheel is allowed to spark out grind the workpiece tothe point Q where the gage indicates that final size is reached. Thewheelhead is then backed off to the point R where the workpiece isremoved and a new workpiece is inserted during the loading portion ofthe cycle. During the sparkout portion of the cycle, it can be seen thatthe wheelhead table 13 is advanced rearwardly in a step-like fashion.This is caused by introducing groups of pulses into the stepping motor28 to retract the stop 37 toward the front of the machine by smallamounts. Since the cylinder 26 keeps the table pressed rearwardly withthe stop 37 contacting the button 42 of the compensating slide (see FIG.2), the effect is to move the wheelhead table rearwardly by the samesmall amounts.

Every time the abrasive wheel removes enough material from the workpieceduring sparkout to lower the load enough so that the hand 111 on theload meter 110 strikes the contact 112, the timer 114 closes the contact116 of the relay for a short period of time and allows a selected numberof pulses to pass to stepping motor No. 2.

In the top part of the chart shown in FIG. 4, the force used from pointB to point C is shown as at an intermediate value. After dress takesplace, grinding occurs from point H to point I at a high force rate.Then, from point N to point 0, the force is at a low value. These forcevalues are selected by supplying the cylinder 26 with fluid at differentvalues in the manner shown and described in the patent of Ware et al.,US. Pat. No. 3,535,828 which issued on Oct. 27, 1970. If the wheelpermitted to sparkout in the conventional manner, the force would dropoff in the manner indicated by the broken line. However, because thewheelhead table is advanced every so often, the force drops off onlyslightly and is then raised upwardly. This alternate raising anddropping of the force is shown by the solid line from point P to pointQ. Although the scale is exaggerated in the drawing, it will beunderstood that the sawtooth pattern is actually a mere ripple and, so,the force is maintained at a substantially constant value. The neteffect is controlled force grinding at a very low value of force.Because the stepping motor is capable of very small increments ofmotion, it is possible to advance the wheelhead table by very smallamounts; in a practical embodiment of the machine, the stop 37 wasadvanced in increments of 0.0000050 inch. It was found that the surfacefinish was excellent and consistent from one workpiece to another,because the wheel had finished the bore at a substantially constantload, thus compensating for variations due to:

1. Cutting conditions on the wheel,

2. Dressing, and

3. The increase of unit pressure because of a smaller worn wheel.

It is obvious that minor changes may be made in the form andconstruction of the invention without departing from the material spiritthereof. It is not, however, desired to confine the invention to theexact form herein shown and described, but it is desired to include allsuch as properly come within the scope claimed.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent is:

l. A grinding machine, comprising a. a base,

b. a workpiece support mounted on the base,

c. a wheelhead support mounted on the base,

d. a wheelhead including a spindle and an abrasive wheel and a motortherefor mounted on the wheelhead support,

e. a feed mechanism for bringing about relative movement between thewheelhead support and the workpiece support to cause engagement of thewheel with the workpiece with a controlled force for most of thegrinding cycle and shifting to sparkout grinding for the remainder ofthe cycle, the feed mechanism including an actuator capable of bringingabout the said relative movement in an incremental manner duringsparkout grinding,

f. a control, including a device for measuring the force on the saidwheelhead spindle, connected to the actuator to advance the wheel towardthe workpiece each time the force drops to a predetermined value, and

4. A grinding machine as recited in claim 3, wherein the controlledforce portion of the grinding cycle is brought about by engagement ofthe wheelhead support with a stop mounted on the base, wherein thestepping motor operates to retract the stop and allow the hydrauliccylinder to press the wheelhead support rearwardly.

5. A grinding machine as recited in claim 4, wherein the said device isa load meter having an adjustable contact operable as a switch tooperate the gate.

1. A grinding machine, comprising a. a base, b. a workpiece supportmounted on the base, c. a wheelhead support mounted on the base, d. awheelhead including a spindle and an abrasive wheel and a motor thereformounted on the wheelhead support, e. a feed mechanism for bringing aboutrelative movement between the wHeelhead support and the workpiecesupport to cause engagement of the wheel with the workpiece with acontrolled force for most of the grinding cycle and shifting to sparkoutgrinding for the remainder of the cycle, the feed mechanism including anactuator capable of bringing about the said relative movement in anincremental manner during sparkout grinding, f. a control, including adevice for measuring the force on the said wheelhead spindle, connectedto the actuator to advance the wheel toward the workpiece each time theforce drops to a predetermined value, and g. a gage connected to thefeed mechanism to terminate the grinding cycle when a predeterminedworkpiece size has been reached.
 1. A grinding machine, comprising a. abase, b. a workpiece support mounted on the base, c. a wheelhead supportmounted on the base, d. a wheelhead including a spindle and an abrasivewheel and a motor therefor mounted on the wheelhead support, e. a feedmechanism for bringing about relative movement between the wHeelheadsupport and the workpiece support to cause engagement of the wheel withthe workpiece with a controlled force for most of the grinding cycle andshifting to sparkout grinding for the remainder of the cycle, the feedmechanism including an actuator capable of bringing about the saidrelative movement in an incremental manner during sparkout grinding, f.a control, including a device for measuring the force on the saidwheelhead spindle, connected to the actuator to advance the wheel towardthe workpiece each time the force drops to a predetermined value, and g.a gage connected to the feed mechanism to terminate the grinding cyclewhen a predetermined workpiece size has been reached.
 2. A grindingmachine as recited in claim 1, wherein the feed mechanism includes ahydraulic cylinder for producing the controlled force.
 3. A grindingmachine as recited in claim 2, wherein the said actuator is a steppingmotor operative to produce incremental motion in response to the receiptof electrical pulses, and wherein the said device operates a gate at thepredetermined load to introduce a preselected number of pulses to theactuator.
 4. A grinding machine as recited in claim 3, wherein thecontrolled force portion of the grinding cycle is brought about byengagement of the wheelhead support with a stop mounted on the base,wherein the stepping motor operates to retract the stop and allow thehydraulic cylinder to press the wheelhead support rearwardly.